Diffraction Grating with Multiple Periodic Widths

ABSTRACT

An integrated circuit includes a substrate, a plurality of photo detectors formed in the substrate, and a diffraction grating having multiple sections disposed over the plurality of photo detectors. Each section of the diffraction grating has a respective periodic width for a respective target wavelength. The diffraction grating has at least two different target wavelengths. The diffraction grating is interlaced with filters. The filters in each section of the diffraction grating are configured to pass a respective electromagnetic wave with the respective target wavelength.

TECHNICAL FIELD

The present disclosure relates generally to an integrated circuit andmore particularly a diffraction grating.

BACKGROUND

A diffraction grating can be formed in an integrated circuit with aperiodic width. For applications such as angle sensitive pixels (ASP),an image of an incident plane wave is repeated at a Talbot length(Z_(T)) and sensors located at the Z_(T) can be used to detect theimage. A diffraction grating that can produce a better image isdesirable.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a cross section diagram of an exemplary integrated circuitincluding a diffraction grating according to some embodiments;

FIG. 2 is a flowchart of the fabrication method of the exemplaryintegrated circuit including in FIG. 1 according to some embodiments;

FIG. 3 is a schematic diagram of an exemplary integrated circuit havingmultiple divisions that include diffraction gratings in FIG. 1 accordingto some embodiments; and

FIGS. 3A-3D are partial cross section diagrams of the exemplaryintegrated circuit in FIG. 3 having different phase between photodetectors and the diffraction grating according to some embodiments.

DETAILED DESCRIPTION

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use, and do notlimit the scope of the disclosure.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

FIG. 1 is a schematic diagram of an exemplary integrated circuit 100including a diffraction grating 124 according to some embodiments. Theintegrated circuit 100 includes a substrate 102, photo detectors 104,dielectric layers 106, 110, 112, 116, and 118, metal layers 108 and 114,and a diffraction grating 124.

The substrate 102 comprises silicon, silicon dioxide, aluminum oxide,sapphire, germanium, gallium arsenide (GaAs), an alloy of silicon andgermanium, indium phosphide (InP), silicon on insulator (SOI), or anyother suitable material. The substrate 102 may further includeadditional features or layers to form various devices and functionalfeatures.

The dielectric layer 106 and the metal layers 108 are formed on thefront side of the substrate 102 in some embodiments, while dielectriclayers 110, 112, 116, and 118, and the metal layer 114 are formed on theback side 103 of the substrate 102 in some embodiments. The dielectriclayers 106, 110, 112, 116, and 118 comprise SiO₂, SiN, low-k dielectric,or any other suitable material and can be formed by chemical vapordeposition (CVD) or other appropriate deposition process, in someembodiments.

In some embodiments, the dielectric layer 110 and 116 comprise SiO₂ asbuffer or protection films and the dielectric layers 112 and 118comprise SiN as protection film. The metal layers 108 and 114 compriseCu, Al, AlCu, or any other suitable material for electrical connectionsor pads, and can be formed by physical vapor deposition (PVD),electrochemical plating, or any other suitable process.

The diffraction grating 124 includes multiple sections 123 a, 123 b, and123 c over the photo detectors 104. Each section 123 a, 123 b, and 123 cof the diffraction grating 124 has a respective periodic width a1, a2,and a3 for a respective target wavelength λ1, λ2, and λ3.

Even though three sections 123 a, 123 b, and 123 c are shown along thecross section in FIG. 1 with three different target wavelengths λ1, λ2,and λ3, there can be different numbers of sections and different numbersof target wavelengths. For example, the diffraction grating 124 can havetwo different target wavelengths, or four or more target wavelengths.

Also, the diffraction grating 124 can have different sections with thesame target wavelengths. For example, the diffraction grating 124 canhave 6 sections along one direction with 3 target wavelengths, where thetarget wavelength of each section is λ1, λ2, λ3, λ1, λ2, and λ3,arranged in that order or any other order. The section width ofdifferent sections 123 a, 123 b, and 123 c may be the same or differentfrom each other in various applications.

The diffraction grating 124 has each grating line 120 comprising metal(e.g., Cu or AlCu), SiN, or SiO₂ that is interlaced with filters 122 a,122 b, and 122 c in a respective section of 123 a, 123 b, and 123 c. Thefilters 122 a, 122 b, and 122 c in each section are configured to pass arespective electromagnetic wave with the respective target wavelength ofλ1, λ2, and λ3 (such as blue, green, and red light).

The filters 122 a, 122 b, and 122 c comprise any suitable material. Inan example, the filters 122 a, 122 b, and 122 c include a dye-based (orpigment-based) polymer or photoresist for filtering out and passingelectromagnetic waves with a specific wavelength (or frequency band).Alternatively, the filters 122 a, 122 b, and 122 c could include a resinor other organic-based material having color pigments. For example, thefilters 122 a, 122 b, and 122 c comprise photoresist or polymer with dyeor pigments, to pass a visible light such as red, green, and blue for anRGB pixel.

The periodic width a1, a2, and a3 can be determined from the followingequation in some embodiments:

$\begin{matrix}{{Z_{T} = \frac{2a^{2}}{\lambda}},} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

where α is the periodic width, λ is the respective target wavelength,and Z_(T) is the Talbot length.

If the target wavelength is comparable to the periodic width, thenperiodic width a1, a2, and a3 can be determined from the followingequation in some other embodiments:

$\begin{matrix}{{Z_{T} = \frac{\lambda}{1 - \sqrt{1 - \frac{\lambda^{2}}{a^{2}}}}},} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

where α is the periodic width, λ is the respective target wavelength,and Z_(T) is the Talbot length.

For example, with a fixed Talbot length at 300 nm, the periodic widthcan be 262 nm for a blue light at wavelength 460 nm, 284 nm for a greenlight at wavelength 540 nm, and 302 nm for a red light at wavelength 610nm. By modifying the periodic width of the diffraction grating 124, thelight image from the diffraction grating 124 can be detected by thephoto detectors 104 at the same distance Z_(T) for electromagnetic waves(e.g. visible light) having different wavelengths with better quantumefficiency. In some embodiments, the period width of the diffractiongrating 124 can be 0.2 μm-0.9 μm for blue light, 0.3 μm-0.95 μm forgreen light, and 0.32 μm-1 μm for red light. The width definition ratiobetween the filter (122 a, 122 b, or 122 c) and the grating line 120 canbe 0.35:0.65-0.65:0.35 in some embodiments.

FIG. 2 is a flowchart of a fabrication method of the exemplaryintegrated circuit 100 in FIG. 1 according to some embodiments. At step202, photo detectors 104 are formed in the substrate 102. Photodetectors 104 can be photo diodes such as PN junction diodes or PINdiodes, and can be formed by depositing P-type and N-type dopants usingion implantation, for example. The periodic width of the photo detectors104 can be different from the periodic width of the diffraction grating124 in some embodiments. In other embodiments, the periodic width of thephoto detectors 104 can be the same or similar to the periodic width ofthe diffraction grating 124.

Afterwards, the substrate 102 can be thinned down on the backside 103 toabout 2 μm by a chemical mechanical polishing (CMP). Dielectric layers110 (e.g., SiO₂) and 112 (e.g., SiN) can be deposited by CVD with thethickness ranging 0.3 μm-0.5 μm and 0.1 μm-0.3 μm respectively in someembodiments. The metal layer 114 (e.g., AlCu) can be deposited by a PVDwith the thickness ranging 0.4 μm-1 μm.

Then the dielectric layers 110 and 112, and the metal layer 114 can beetched out for the diffraction grating 124 (also called a pixel area insome applications). Before forming the diffraction grating 124,dielectric layers 116 (e.g., SiO₂) and 118 (e.g., SiN) can be depositedby CVD with a thickness ranging 0.2 μm-0.5 μm and 0.1 μm-0.2 μmrespectively in some embodiments.

At step 204, the diffraction grating 124 is formed with multiplesections 123 a, 123 b, and 123 c over the photo detectors 104. For thegrating lines 120, a metal layer (e.g., Cu or AlCu) can be deposited byPVD or a dielectric layer (e.g., SiO₂) can be deposited by CVD with athickness ranging 0.3 μm-0.8 and the grating line 120 pattern can beetched out by photolithography.

Afterwards, filter material can be filled in for the filters 122 a, 122b, and 122 c by coating, for example. The filters 122 a, 122 b, and 122c are interlaced with the grating lines 120 of the diffraction grating124. The filters 122 a, 122 b, and 122 c can comprise any suitablematerial. In an example, the filters 122 a, 122 b, and 122 c include adye-based (or pigment-based) polymer or photoresist for filtering outand passing electromagnetic wave with a specific wavelength (orfrequency band). Alternatively, the filters 122 a, 122 b, and 122 ccould include a resin or other organic-based material having colorpigments. For example, the filters 122 a, 122 b, and 122 c comprisephotoresist or polymer with dye or pigments, to pass a visible lightsuch as red, green, and blue for an RGB pixel.

Each section 123 a, 123 b, and 123 c of the diffraction grating 124 hasa respective periodic width a1, a2, and a3, for a respective targetwavelength λ1, λ2, and λ3. The filters 122 a, 122 b, and 122 c in eachsection of the diffraction grating 124 are configured to pass arespective electromagnetic wave with the respective target wavelength.The definition ratio between the filter (122 a, 122 b, or 122 c) and thegrating line 120 can be 0.35:0.65-0.65:0.35 in some embodiments.

There can be different numbers of sections and different numbers oftarget wavelengths. For example, the diffraction grating 124 can havetwo different target wavelengths, or four or more target wavelengths.The section width of 123 a, 123 b, and 123 c may be the same ordifferent in various applications.

FIG. 3 is a schematic diagram of an exemplary integrated circuit 300having multiple divisions 302, 304, 306, and 308 that includediffraction gratings such as 124 in FIG. 1 according to someembodiments. The cross section of the integrated circuit 300 along cutlines A-A′ and B-B′ can be similar to FIG. 1. In some embodiments, thediffraction grating 124 can have 6 sections along the cut lines A-A′ andB-B′, 3 sections in each division of 302, 304, 306, and 308 with 3target wavelengths.

For example, the target wavelength of each section can be arranged inthe order of λ1, λ2, λ3, λ1, λ2, and λ3, or any other order along thecut lines A-A′ and B-B′. Each division of 302, 304, 306, and 308 canhave a different phase between the photo detectors 104 and filters 122(or grating lines 120) as shown in FIGS. 3A-3D.

FIGS. 3A-3D are partial cross section diagrams of the exemplaryintegrated circuit 300 in FIG. 3 having different phase between photodetectors and the diffraction grating according to some embodiments. InFIG. 3A, the photo detectors 104 are aligned with the filters 122 of thediffraction grating 124 with a phase difference of 0 degrees. In FIG.3B, the photo detectors 104 are aligned with the filters 122 of thediffraction grating 124 with a phase difference of 90 degrees. In FIG.3C, the photo detectors 104 are aligned with the filters 122 of thediffraction grating 124 with a phase difference of 180 degrees. In FIG.3D, the photo detectors 104 are aligned with the filters 122 of thediffraction grating 124 with a phase difference of 270 degrees.

In one example, the division 302 in FIG. 3 has the alignment with 0degrees phase difference as shown in FIG. 3A, the division 304 in FIG. 3has the alignment with 180 degrees phase difference as shown in FIG. 3C,the division 306 in FIG. 3 has the alignment with 270 degrees phasedifference as shown in FIG. 3D, and the division 308 in FIG. 3 has thealignment with 90 degrees phase difference as shown in FIG. 3B. Anyother phase arrangement is possible in various applications, includingdifferent number of phases (e.g., 8 phases instead of 4 phases) anddifferent phase locations in the integrated circuit 300.

According to some embodiments, an integrated circuit includes asubstrate, a plurality of photo detectors formed in the substrate, and adiffraction grating having multiple sections disposed over the pluralityof photo detectors. Each section of the diffraction grating has arespective periodic width for a respective target wavelength. Thediffraction grating has at least two different target wavelengths. Thediffraction grating is interlaced with filters. The filters in eachsection of the diffraction grating are configured to pass a respectiveelectromagnetic wave with the respective target wavelength.

According to some embodiments, a method includes forming a plurality ofphoto detectors in a substrate. A diffraction grating with multiplesections is formed over the photo detectors. Each section of thediffraction grating has a respective periodic width for a respectivetarget wavelength. The diffraction grating has at least two differenttarget wavelengths. The diffraction grating is interlaced with filters.The filters in each section of the diffraction grating are configured topass a respective electromagnetic wave with the respective targetwavelength.

According to some embodiments, an integrated circuit includes asubstrate and a plurality of divisions of the substrate. Each divisionincludes a plurality of photo detectors formed in the substrate and adiffraction grating having multiple sections disposed over the pluralityof photo detectors. Each section of the diffraction grating has arespective periodic width for a respective target wavelength. Thediffraction grating has at least two different target wavelengths. Thediffraction grating is interlaced with filters. The filters in eachsection of the diffraction grating are configured to pass a respectiveelectromagnetic wave with the respective target wavelength. Therespective photo detectors in each division are aligned with therespective diffraction grating with a different phase from anotherdivision.

A skilled person in the art will appreciate that there can be manyembodiment variations of this disclosure. Although the embodiments andtheir features have been described in detail, it should be understoodthat various changes, substitutions and alterations can be made hereinwithout departing from the spirit and scope of the embodiments.Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, and composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosed embodiments, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure.

The above method embodiment shows exemplary steps, but they are notnecessarily required to be performed in the order shown. Steps may beadded, replaced, changed order, and/or eliminated as appropriate, inaccordance with the spirit and scope of embodiment of the disclosure.Embodiments that combine different claims and/or different embodimentsare within the scope of the disclosure and will be apparent to thoseskilled in the art after reviewing this disclosure.

What is claimed is:
 1. An integrated circuit, comprising: a substrate; aplurality of photo detectors formed in the substrate; and a diffractiongrating having multiple sections disposed over the plurality of photodetectors, wherein each section of the diffraction grating has arespective periodic width for a respective target wavelength, thediffraction grating has at least two different target wavelengths, thediffraction grating is interlaced with filters, and the filters in eachsection of the diffraction grating are configured to pass a respectiveelectromagnetic wave with the respective target wavelength.
 2. Theintegrated circuit of claim 1, wherein the plurality of photo detectorsare located at a Talbot length away from the diffraction grating.
 3. Theintegrated circuit of claim 2, wherein the periodic width, the targetwavelength, and the Talbot length are related as expressed in theequation${Z_{T} = \frac{2a^{2}}{\lambda}},{{{or}\mspace{14mu} Z_{T}} = \frac{\lambda}{1 - \sqrt{1 - \frac{\lambda^{2}}{a^{2}}}}},$wherein α is the periodic width, λ is the target wavelength, and Z_(T)is the Talbot length.
 4. The integrated circuit of claim 1, furthercomprising at least one dielectric layer between the plurality of photodetectors and the diffractive grating.
 5. The integrated circuit ofclaim 4, wherein the at least one dielectric layer comprises SiO₂, SiN,or any combination thereof.
 6. The integrated circuit of claim 1,wherein the plurality of photo detectors and the diffraction gratinghave the same periodic widths.
 7. The integrated circuit of claim 6,wherein the plurality of photo detectors are aligned with thediffraction grating with a phase difference by 0 degrees, 90 degrees,180 degrees, 270 degrees, or any combination thereof.
 8. The integratedcircuit of claim 1, wherein the diffraction grating comprises Cu, AlCu,SiN, or SiO₂.
 9. The integrated circuit of claim 1, wherein the filterscomprise photoresist or polymer.
 10. The integrated circuit of claim 1,wherein the photo detectors are PN junction diodes.
 11. A method,comprising: forming a plurality of photo detectors in a substrate; andforming a diffraction grating with multiple sections over the photodetectors, wherein each section of the diffraction grating has arespective periodic width for a respective target wavelength, thediffraction grating has at least two different target wavelengths, thediffraction grating is interlaced with filters, and the filters in eachsection of the diffraction grating are configured to pass a respectiveelectromagnetic wave with the respective target wavelength.
 12. Themethod of claim 11, further comprising forming at least one dielectriclayer between the plurality of photo detectors and the diffractiongrating.
 13. The method of claim 12, wherein the at least one dielectriclayer comprises SiO₂, SiN, or any combination thereof.
 14. The method ofclaim 11, further comprising thinning a backside of the substrate afterforming the plurality of photo detectors.
 15. The method of claim 11,wherein the diffraction grating is formed at a Talbot length away fromthe plurality of photo detectors.
 16. The method of claim 11, whereinthe plurality of photo detectors are PN junction diodes.
 17. The methodof claim 16, wherein the PN junction diodes are formed by ionimplantation.
 18. The method of claim 11, wherein the diffractiongrating comprises Cu, AlCu, SiN, or SiO₂.
 19. The method of claim 11,wherein the filters comprise photoresist or polymer.
 20. An integratedcircuit, comprising: a substrate; a plurality of divisions of thesubstrate, wherein each division includes: a plurality of photodetectors formed in the substrate; and a diffraction grating havingmultiple sections disposed over the plurality of photo detectors,wherein each section of the diffraction grating has a respectiveperiodic width for a respective target wavelength, the diffractiongrating has at least two different target wavelengths, the diffractiongrating is interlaced with filters, the filters in each section of thediffraction grating are configured to pass a respective electromagneticwave with the respective target wavelength, and the respective pluralityof photo detectors in each division are aligned with the respectivediffraction grating with a different phase from another division.